Sept. 10, 2010 -- Some runners swear by their pre-run stretch as a sure-fire way to run better and stronger and reduce their risk of injury in the process.

But according to a new study, distance runners who stretch before a run may not perform as well and may spend more energy than runners who skip the stretch.

"Overall, I don't think it's worth it to stretch before a run," researcher Jacob M. Wilson, PhD, assistant professor of exercise science and sport studies at the University of Tampa, tells WebMD. "After a run, if someone is trying to work on flexibility, that's fine."

Although his study was done only on male runners who were young and highly trained, Wilson speculates that the findings would apply to recreational runners and to female runners as well.

The study is published in the Journal of Strength and Conditioning Research.

Stretching Before a Run: The Study

Wilson evaluated 10 runners, all men, who were on average 25 years old. They were in good shape with a low percent of body fat -- just under 7%, on average.

All runners participated in a 60-minute treadmill run on two different days separated by at least one week. One time, they stretched for 16 minutes before running and the other time they just sat quietly for the same time period.

The pre-run stretches were static -- stretching a muscle to the maximum length and holding it -- and included all the major muscle groups of the lower body.

After the stretching or the sitting, the runners did a 30-minute warm-up run, then a 30-minute performance run. Each time, the runners were told to run as far as possible during the performance part, but they couldn't see distance or speed on the treadmill display panel.

Without stretching, the runners averaged 6 kilometers or 3.7 miles in the half-hour performance run, Wilson tells WebMD. With stretching, they averaged 5.8 km or 3.6 miles, a difference of 3.4%.While the difference seems small, it could add up during a competitive event.

Previous research by others has looked at stretching and the effects on sprinting or vertical jumping, Wilson says. "Ninety percent have found declines in performance."

He says that "ours is one of the first to look at stretching and endurance performance, and we saw decrements."

Stretching also resulted in a higher number of calories burned. When runners stretched before they ran, they burned 425 calories, on average, during the warm-up run. When they didn't stretch, they burned 405 calories, on average.

Stretching and Performance

Whether to stretch before running or not is "an individual choice," says Ryan Lamppa, a spokesman for Running USA, which promotes the growth of the U.S. running industry. He has coached distance runners and is a runner.

"I know runners of all abilities," he says. "Some stretch on a regular basis and some don't. Many, like me, stretch after a run, when the muscles are warm and supple."

"This study reinforces what I've heard in the sport at the top end: 'You don't see a cheetah stretch before the cat goes after [its] prey.'"

"This [study] is looking at a very select group of people," says Cathy Fieseler, MD, member of the board of directors of the American Medical Athletic Association and a veteran marathoner and ultra-distance runner. A doctor in Tyler, Texas, she notes that the men studied had a low level of body fat and were regular runners. She says the finding that the pre-run stretch affected performance in high-level athletes is plausible, but she is not sure if the findings would apply to recreational or older runners.

She wonders, too, if the 16-minute stretching period made the runners more tired than the pre-run session of simply sitting, and if that may have affected performance.

The research is clear, she says, on another aspect of stretching. "There's no study that says a pre-run stretch reduces the risk of injury."

Her advice for endurance runners? She usually doesn't recommend a pre-run stretch, but she does see the value of warming up. She tells runners: "Start off easy, do a mile or two. If you are sweating, your muscles are warmed up. Then you can pick up the pace."